This invention relates to the field of retroreflectors, and more particularly, to a retroreflector assembly mounted on a flexible, vibration and shock absorbing mounting assembly.
Retroreflectors are old in the art. Corner cube retroreflectors are made of three plates joined together having optically flat reflective surfaces disposed at right angles to each other, and meeting at what can be described as a common inside corner of an imaginary cube. Retroreflectors in general have the essential property of causing incident and reflected light rays to travel along parallel paths.
When corner cube retroreflectors are assembled for high accuracy and precision it is always essential to ensure that the reflective surfaces remain mutually perpendicular. This is especially difficult when the retroreflector is used in applications where large vibrational stresses are applied to the structure of the retroreflector. In these situations, it is not uncommon for the structural components of the retroreflector to become loose from each other, thereby changing the orientational alignment of its components and hence reducing the accuracy of the retroreflector.
Accordingly, in addition to the normal effects on the perpendicularity of the reflective surfaces by external stresses such as thermal expansion or contraction of the substrate material from which the retroreflector is made, and/or deflection caused by curing of the adhesives which join members of the retroreflector and/or mass, it has been determined that vibrations translated into the body of the retroreflector will cause the retroreflector to rapidly deteriorate in its integral construction thereby requiring replacement of this expensive unit. Accordingly, it would be desirable to mount a retroreflector in such a manner as to reduce these vibrational stresses. Further, it would be desirable to be able to mount a retroreflector in such a manor that bending is only allowed in the mount in the axial direction, and not rotationally or radially, as radial or rotational movements can effect beam path location, while axial movement does not. Examples of corner cube retroreflector mounting assemblies that have proven successful in maintaining the reflective surfaces in their perpendicular orientations, but have done nothing to reduce vibrational stresses from traveling into the structure of the retroreflector, are:
U.S. Pat. No. 3,977,765, to Lipkins, which discloses a corner cube retroreflector mounted to a support structure through means of applying an adhesive into the joints formed between joined members of the retroreflector and a flat surface of the support structure. This method of mounting the retroreflector ensures that the stresses associated with the curing of the adhesive are primarily translated along the reflective surfaces, not in such a manner as to cause deflection of those surfaces.
U.S. Pat. No. 5,122,901, to Bleier, which discloses a surveying retroreflector assembly having a corner cube retroreflector mounted within a receptacle. The receptacle has a conically configured interior for receiving the retroreflector and for maintaining the perpendicular alignment of the reflective surfaces of the plates of the retroreflector. The receptacle is then received within an outer casing to allow for mounting of the entire assembly.
U.S. Pat. No. 5,335,111, to Bleier, which discloses a corner cube retroreflector assembly with a hard mount assembly. Through this structure, the retroreflector is adhered to a mounting member in such a way that the reflective surfaces of the retroreflector are not subject to distortional deflections due to common stresses such as those due to thermal expansion/contraction, curing or mass. This mounting method also reduced movement of the retroreflector and allowed for easy and secure mounting of the retroreflector to a support.
In accordance with the invention, a flexible mount assembly is provided for a corner cube retroreflector assembly. The mounting assembly of the invention receives a retroreflector in such a way as to reduce deflection of the reflective surfaces of the retroreflector due to stresses from vibration or jolts to the structure and in such a way as to prevent radial and/or rotational bending/movement of the retroreflector from the vibrations, so that beam path variations are prevented. The mounting assembly also allows for easy and secure mounting of the retroreflector to a support.
The corner cube retroreflector usually has three plates having optically flat reflective surfaces disposed at right angles to each other and non-reflective surfaces opposite to the reflective surfaces of the plates. Each of the plates also has first and second sides disposed at right angles to each other, the first side of each plate abutting and being adhered to the reflective surface of the plate adjacent to it.
The mounting member has a base member comprising three radial arms situated at substantially 120xc2x0 from each other. In a preferred embodiment, a connector is mounted to the end of each arm, with the connector connecting the arm of the base to a resilient support member. Each support member has a pair of co-planar receiving surfaces, for receipt thereon of a mounting block, which mounting block is adhered to the underside (non-reflective side) of the retroreflector in the groove formed between the joined plates. The co-planar receiving surfaces of each of the support members are separated by a notch in the structure of the support member. In substantial part, it is the formation of the notch that allows the support member to be resilient (i.e., flexible when under vibrational stresses) in the axial direction.
In other embodiments, the radial arms of the mounting member and the connectors can be uniformly formed members. In this way, out of the end of each arm there would integrally extend the connectors. Another embodiment could have the mounting blocks an integrally formed part of the support members; i.e., integrally extending out from the co-planar surfaces. In yet further embodiments, the mounting blocks could be a pair of mounting blocks for each support member, instead of a single mounting block that spans the notch under and between the co-planar receiving surfaces. Under any of these constructions, the manner of the mounting of the retroreflector to the mounting member ensures rotational and radial rigidity, while only allowing for axial bending/movement of the retroreflector. Hence beam and path location is not effected.
The base member of the mounting member also has a threaded bore extending therein for receipt of a correspondingly threaded member extending from a support structure. In the alternative, the base member could have the male, threaded extending member, while the support structure has the receiving female threaded bore. This system ensures easy and secure mounting to any support structure.
Accordingly, it is an object of the invention to provide an improved vibration and shock absorbing mounting assembly for a corner cube retroreflector assembly.
Another object of the invention is to provide an improved vibration and shock absorbing mounting assembly for a corner cube retroreflector assembly which causes minimal external stresses to the reflective surfaces of the retroreflector from the mounting.
Still another object of the invention is to provide an improved vibration and shock absorbing mounting assembly for a corner cube retroreflector assembly wherein the assembly achieves significant reductions in rotational and radial movement of the assembly in order to achieve high-accuracy measurements, even under extreme vibrational stresses.
Yet a further object of the invention is to provide an improved vibration and shock absorbing mounting assembly for a corner cube retroreflector assembly wherein the mounting of the entire assembly to a support structure is easy and secure.
Other objects of the invention will in part be obvious and will in part be apparent from the following description.
The invention accordingly comprises an assembly possessing the features, properties and relation of components which will be exemplified in the constructions hereinafter described, and the scope of the invention will be indicated in the claims.